1. Field of the Invention
The present invention relates to sewing yarn comprising at least one multifilament yarn whose mutually twisted-together individual filaments are made of a thermoplastic polymer.
2. Discussion of the Background
Sewing yarns for industrial materials, such as tarpaulins, seat covers and glass fabrics, but also for leather and plastics are customarily based on polyesters.
However, such sewing yarns have the disadvantage of a comparatively low melting point, so that they can only be processed on high-speed sewing machines, in particular automatic sewing machines where abrupt change in the sewing speed can make the sewing yarns very hot, if they have been provided with a special finish. In addition, polyester fibers are not sufficiently hydrolysis- and solvent-resistant for many purposes.
A higher temperature resistance is one of the properties of sewing yarns made of aromatic polyamide (Kevlar.RTM.). However, they are expensive to produce; moreover, their mechanical properties are fixed by the process of manufacture (solvent spinning), so that they can only be varied within narrow limits and cannot be adapted to changing requirements. Furthermore, they are very difficult to dye. Such sewing yarns have therefore not become important in the field.
It is known that polyether ketones can be spun from the melt into fibers and then be drawn. A suitable spinning process is described for example in EP-A-202 082. The resulting multifilament yarns have a wide range of properties. For instance, the linear density of the individual filament can range from 2.8 to 100 denier (corresponding to 2.5 to 90 dtex), and the elongation at break can be 15-200%. However, it is not stated that such fibers can be used to produce sewing yarns and which multifilament yarns are particularly suitable for that purpose.